1. Field of the Invention
The present invention relates to a wire electric discharge machine having a taper angle correction function using a contact detector and a calculation method for wire support positions of a wire electric discharge machine.
2. Description of the Related Art
When a taper machining is performed on a workpiece by a wire electric discharge machine, the wire support positions of the upper and lower wire guides for supporting the wire electrode are measured by a jig or the like through short-circuit detection of the wire electrode, and the measured wire support positions are set in the controller.
A known technique for correcting the angle of a wire electrode is disclosed in Japanese Patent Application Laid-Open No. 2000-24839. In this technique, the taper angle is corrected through contact of a wire electrode by using a specific jig without performing machining actually. Another known technique for automatically plumbing a wire electrode is disclosed in Japanese Patent Application Laid-Open No. 11-320266.
If electric discharge machining of a workpiece is performed actually, the bending of the wire electrode is increased due to discharge heat, error is included in the taper angle, and the machining precision degrades. In the above technique disclosed in Japanese Patent Application Laid-Open No. 2000-24839, no effects of electric discharge machining are considered, so the machining precision of a machined object degrades. In addition, measurement of the workpiece is not made on the electric discharge machine, so additional machining or subsequent finishing is not supported. The technique disclosed in Japanese Patent Application Laid-Open No. 11-320266 is applicable only to the correction of the angle of a wire electrode, so it is not applicable to tapering in which the correction of both the angle and dimensions is performed.
As described above, the prior art method performs tapering by measuring the support positions (hereinafter referred to as wire support positions) of a wire electrode using a jig before machining and setting the measured data in the controller. Upon completion of tapering, the machined object is measured by a measuring instrument such as a tool maker's microscope or three-dimensional measuring instrument, a correction value is calculated from the measured error, the calculated measurement value is input to the controller, and then re-machining is performed.
Accordingly, the prior art technique is inconvenient in that a measuring instrument is required separately from a wire electric discharge machine and a correction value needs to be calculated according to a mathematical expression. In addition, if a machined workpiece is removed from a wire electric discharge machine, predetermined measurement is performed, and the machined workpiece is mounted on the wire electric discharge machine again, then a deviation arises between the previous and current mounting positions. This makes it very difficult to perform re-machining such as modification after measurement.